Title: Override process control system

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Abstract: An override process control system for regulating a process with a single final control element, such as a valve, from two or more process variables that are interdependent and must not exceed acceptable minimum and maximum limits. The system includes a like number of electronic controllers each acting to compare a respective process variable with a set point to produce an output signal reflecting the deviation of the process variable from the set point. The primary controller responsive to the process variable directly influenced by the setting of the final control element has its output signal applied thereto to regulate this element, whereas the other controllers which are responsive to secondary process variables operate on a standby basis. Coupled by individual lines to the several controllers is an override selector station which monitors the operation of the controllers, and in the event an unsafe signal is received from one of the standby controllers, forces the primary controller to respond to the unsafe signal until such time as the signal is again safe.


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